Proper treatment of agricultural crops has long been recognized as having an important and direct effect on the healthy emergence and maintenance of the crops. It is therefore a common agricultural technique to discharge granular agricultural treating agents, such as pesticides, herbicides, fertilizer and the like, to control pests, weeds and various fungi which may otherwise damage or even ruin the crops. The application of such chemicals, however, should be accurately and uniformly distributed over the area intended to be applied. This is particularly true of chemicals which are selective in their action. For example, excessive application in any given area results in the loss of expensive chemicals and may lead to crop loss. Moreover, such application may have an adverse environmental impact. Of course, insufficient application results in the lack of adequate treating agent; thus, for example resulting in inadequate pest control.
In addition, it is desirable to control application of such treating agents to account for various concentrations of granular material intended to be applied and in consideration of varying operating conditions. For example, in some applications, it is desirable to apply the material to preselected areas of the crop only. Further, the rate of delivery, i e., the output of the treating agent over a given unit of time, must be easily adjusted to account for variations in the crop and in the soil type and in the terrain as well as variations in the speed of applicating equipment.
Previously proposed granular materials applicators typically operate with the use of an auger that rotates for removal of the granular material, or apertures closed by slide valves of the type found in small commercially available lawn fertilizers, or even brushes extending into a hopper containing the granular material. In some of the devices, material flows from a hopper to form piles which are thereafter discharged. The tops of the piles may, for example, be displaced into channels leading to spreaders by a reciprocating rod extending the length of the hopper and studs or washers on the rod. The result, however, is cyclical output. Moreover, on rough terrain, the piles forming in the hopper tend to become displaced or are inadvertently dispensed which may cause over-application or wasting of expensive chemicals.
Other known applicators include trapdoor type devices extending the length of the hopper for rocking back and forth to open one side of the hopper and then the other. Such rocking results in intermittent output. In addition, metering devices placed inside the hopper tend to pulverize the granular material, causing compaction within the hopper and reduced feed through the discharge orifices.
Still other applicators provide control for the granular material flow rate with the use of rotating wheels spaced from respective orifices at the base of a hopper. In one arrangement of this type, a rotating wheel is driven with the use of a variable speed electric motor and feedback circuitry to maintain a constant angular velocity of the metering wheels, from which the application rate may be manually adjusted. However, inasmuch as the metering wheels are spaced from the hopper orifice, the system may inadvertently dispense material. Moreover, manual adjustment for changing conditions renders this arrangement somewhat inflexible.
Thus, while prior art applicating systems may function satisfactorily under certain conditions, they are susceptible to irregular and uneven material application, particularly when operating at high rates of speed or over great periods of time. As a result, the material will not be distributed as evenly as intended. Moreover, many of the known material applicators are not capable of accommodating various topologies and continuously variable operating conditions. Further, the known systems do not easily accommodate changes in the type of material or the amount of material desired to be dispensed.